1. Field of Invention
A conveyor anti-runaway apparatus is provided for a conveyor of the type driven by an electric motor connected to a source of electrical power.
2. Prior Art
A common problem which occurs in connection with use of large industrial conveyors, such as those used in automotive assembly plants, is sporadic large increases in conveyor speed. Such speed increases endanger the safety of assembly operators.
In order to resolve this problem, devices termed "conveyor anti-runaways" have been provided. These devices sense, by various means, conveyor chain speeds and detect sudden increases in conveyor speed. Conventionally, such devices automatically physically jam the conveyor chain and stop all movement when the conveyor speed reaches unacceptable levels. Increased conveyor speed can be caused by various conditions. For example, a production part may fall from the conveyor and become wedged between the conveyor chain rollers and the channel that the chain follows. Very large forces can then build up in the conveyor chain drive motor causing the chain to stretch. When the stretching force overcomes the wedged production part, the chain is suddenly released with thousand of pounds of force. In a manner similar to shooting a rubber band, the chain speed increases to dangerous velocities. All assembly workers near the conveyor are endangered as they may be struck and injured by the conveyor or by production parts on the conveyor.
Standard anti-runaway devices have been effective in the past. However, one problem encountered in connection with such devices is that they have required rather extensive time to permit restarting of production. For example, such restart time may be thirty-five minutes with two millwrights and one electrician working together. This down time results in lost production and constitutes a very substantial monetary loss. In accordance with the present invention, a conveyor anti-runaway apparatus is provided which is effective in operation but which requires only a short time to permit restart, for example, about two minutes.